This invention relates generally to the production of concentrated solutions, and, more particularly, to a method and an apparatus for forming a concentrated solution, of a prescribed concentration of solute in a solvent, from a comparatively dilute solution.
Innumerable chemical applications require concentrated solutions of a solute dissolved in a solvent. Each application has unique requirements for the type of it solute, the type of solvent, and the concentration of the solute in the solvent. Such solutions, however, are generally available only in a limited number of concentrations from traditional suppliers. The ability to vary a solution""s concentration is therefore an important art for a wide variety of applications.
The concentration of a solution can be increased through the addition of more solute, or the evaporation of solvent from the solution. In the case of some solutions, such as radioactive solutions, additional solute is often not readily available, and thus the addition of more solute is not practicable. These solutions require evaporative concentration methods.
In conventional evaporative concentration methods, the solution is located in a container, such as a beaker. The solvent is then evaporated, preferably with the addition of heat, and the level of solution in the container thus goes down to an appropriate level for a smaller volume of solution. As the solution evaporates, solute precipitates out onto the container walls above the reduced level of the solution, leaving a crust of dry precipitate where the solution level receded. This precipitation removes solute from the solution, limiting both the efficiency and the accuracy of concentration. These problems are exacerbated when dealing with hazardous and/or costly solutions, such as solutions containing radioactive solutes, in that the quantity of precipitated solute is unknown, and it is difficult to efficiently recover the solute in a practical form.
Accordingly, there has existed a definite need for a method, and related apparatus, to concentrate a solute in solution with a solvent without significant precipitation of the solvent. The present invention fulfills this need and provides further related advantages.
The present invention provides a method, and an apparatus, for forming a prescribed concentration of a substance in a mixture with a fluid, from a comparatively dilute mixture. The mixture is most preferably a solution of a solute in a solvent. The following summary and description generally discuss the invention in terms of a particularly preferred solution and a preferred use for that solution; however, in its broadest embodiments, the invention encompasses both the use for other solutions, and the use for a suspension of a solid substance in a fluid to form a mixture (which can also be referred to as a slurry). The inventions provides for significant economic, safety and quality benefits over conventional evaporative systems.
The apparatus of the invention features a syringe configured to pass the dilute solution through an orifice to form a suspended globule (such as a droplet) of the dilute solution from which solvent is evaporated. The apparatus is configured such that the suspended globule is in contact with sufficiently little solid material to avoid significant precipitation and plating of solute as the solvent evaporates. Preferably, the solution becomes suspended as a drop hanging by surface tension forces from a flat, horizontal, contact surface surrounding the orifice. The orifice adjoins a narrow passageway that is configured to substantially prevent concentration gradient diffusion from the evaporating dilute solution as it becomes concentrated. The apparatus of the invention preferably also features a measuring device, such as a laser micrometer, configured to gauge the amount of suspended solution, as well as a heater configured to provide a stream of heated gas to the suspended solution to accelerate the evaporation of solvent from the solution.
The inventive method and apparatus provide significant advantages over known methods and apparatus, such as the known method of simply evaporating solvent from a solution contained in a container. For the inventive method and apparatus, the suspended solution has little contact with a solid contact surface, thus minimizing the solid surface on which plating can occur. Furthermore, the area of contact is substantially constant, and thus remains wet. This advantage is particularly beneficial when the relevant solution is difficult to handle, such as is the case for radioactive solutions.
The invention also features monitoring the size of the suspended solution, and further features passing additional dilute solution from the orifice to maintain the size of the drop between a prescribed minimum size and a prescribed maximum size, during evaporation of the solvent. The monitoring and emission continue until the drop has reached the prescribed concentration. These features advantageously provide for the concentration of substantially larger quantities of solution to substantially higher concentration levels within the natural limitations on drop size (i.e., the limitations on the amount of weight that the surface tension forces can support). These features also provide for little to no precipitation losses of solute during evaporation of the solvent.
Additionally, the invention features a computerized control system that, in combination with the syringe, the measuring device and the heater, advantageously provides for the production of extremely accurate quantities of solution that are concentrated to very specific concentrations.